I didn't care for how the last episode ended, and unfortunately my reason why makes me sound like a nerdy comic book elitist. While the event that ended that plot arc was the same, ie- the zombies in the barn get out, the reason why was different. In the comics, iirc, they got out as more were being put in, making the resulting carnage the result of, depending on your reading, ignorance, naivety, or possibly just false hope. No one in the main cast caused it, and it was made clear that the disaster was inevitable.

In the tv series, Shane opened the door. If Shane hadn't done that, for all we know the barn may have actually been more than capable of containing the zombies. Maybe Hershel's family really did have everything perfectly under control, and Shane just screwed everything up for them. Changing the circumstances changes the subtext.